Add small utility methods in Shell

- ShellTaskOrganizer#getRunningTasks() to get tasks on all the
  displays.
- TaskViewTransitions.isTaskViewTask() to detect if the given
  task is running in a task view.

Flag: EXEMPT bugfix
Bug: 355532757
Test: m
Change-Id: I9b6cc3d4a08c0e42c8db593eda52e6459522af0e